Pellet mill for wet powdery materials

ABSTRACT

A ROTARY EXTRUSION-TYPE PELLET MILL WHEREIN A ROLLER COOPERATING WITH A ROTATING DIE IS FORCIBLY ROTATED BY A GEAR PROVIDED ON THE SURFACE THEREOF IN ENGAGEMENT WITH A GEAR PROVIDED ON THE INSIDE WALL SURFACE OF SAID ROTATING DIE AND THE INTERIOR OF SAID ROLLER IS MAINTAINED PRESSURIZED BY A PRESSURE FLUID SUPPLIED THEREIN FROM THE REAR END OF A ROLLER SUPPORTING SHAFT THROUGHOUT THE PERIOD OF OPERATION, WHEREBY A LOWERING OF EXTRUDING CAPACITY AND FORMATION OF UNSATISFACTORY PRODUCT DUE TO IDLING OR BINDING OF THE ROLLER AS HAS BEEN EXPERIENCED IN A CONVENTIONAL MILL OF THIS TYPE CAN BE ELIMINATED.

.JNM 5' 1971 K ozl MIYAKAWA ETAL 3,551,950

PELLET MILL FOR WET POWDERY MATERIALS Filed Aug. 12. 196e INVENTORS Kwai M .iakaw BYSN; l-gosmd CWfbarb @hm ATTORNEYS ilnited States Patent O PELLET MILL FOR WET POWDERY MATERIALS Kozi Miyakawa and Shimpei Yoshida, Niigata-shi, Japan,

assignors to `l'apan Gas Chemical Company, Inc.,

Tokyo, Japan, a corporation of Japan Filed Aug. 12, 1968, Ser. No. 751,793 Int. Cl. B29f 3/012 U.S. Cl. 18-12 3 Claims ABSTRACT F THE DISCLOSURE A rotary extrusion-type pellet mill wherein a roller cooperating with a rotating die is forcibly rotated by a gear provided on the surface thereof in engagement with a gear provided on the inside wall surface of said rotating die and the interior of said roller is maintained pressurized by a pressure fluid supplied therein from the rear end of a roller supporting shaft throughout the period of operation, whereby a lowering of extruding capacity and formation of unsatisfactory product due to idling or binding of the roller as has been experienced in a conventional mill of this type can be eliminated.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to an improved extrusiontype pellet mill for wet powdery materials.

EDescription of the prior art A conventional extrusion-type pellet mill is so constructed that a roller disposed in a rotary hollow cylinder having a multiplicity of apertures bored through the wall thereof rotates in sliding contact with the inside wall surface of said hollow cylinder, and a powdery material fed into said hollow cylinder is compressed between said roller and the inside wall surface of said cylinder and extruded through said apertures in the form of pellet.

The present inventors attempted to produce a pellet of a fertilizer, e.g a high-analysis compound fertilizer, by extrusion using the conventional extrusion-type pellet mill of the construction described above and found that the conventional pellet mill had the following defects. Namely, in the conventional pellet mill, since the perforated hollow cylinder only is rotated and the roller is driven by said cylinder in sliding contact therewith, the roller frequently stops rotating by being bound by a powdery material being processed depending upon the type of material and as the result a satisfactory extrusion of the powdery material through the perforated Wall of the cylinder cannot be obtained due to a lack of compressive force. In addition, since the conventional pellet mill resorts only to the compressive force for forcibly extruding the material through the apertures, the hollow cylinder is required to be rigid and tough sucient to withstand the high pressure exerted thereon and accordingly a large power is consumed for the pellet-making operation.

Furthermore, in the operation of the conventional pellet mill, the powdery material being processed tends to intrude into a roller supporting mechanism housed in said roller, interferring with the smooth rotation of the roller or causing a malfunction of the same. In order to avoid such troubles, therefore, it becomes necessary to interrupt the operation every several hours and to force into the roller a lubricant, such as grease, and thereby to purge the powdery material from the roller along with said lubricant. By this reason, the conventional pellet mill is capable of continuous operation of only four or ive hours at longest.

3,551,950 Patented Jan. 5, 1971 SUMMARY OF THE INVENTION The object of the present invention is to provide a pellet mills which is free from the aforesaid drawbacks of the conventional one. The pellet mill of the present invention comprises a rotary, perforated, hollow cylinder having a gear formed integrally on the inner wall surface thereof, a roller disposed inside of said hollow cylinder and having a gear formed integrally on the outer surface thereof for engagement with the gear of said hollow cylinder, said roller being rotated forcibly by said rotary hollow cylinder through the engagement of said gears, whereby a powdery material fed in said hollow cylinder is extruded into the form of pellet through the perforated wall of said cylinder while being compressed and kneaded between said roller and said cylinder, and means for supplying and retaining a pressure uid in the interior of said roller to prevent intrusion of the powdery material into said roller.

BRIEF DESCRIPTION OF THE DRAWING FIG. l is a schematic view, in cross-section, of the pellet mill according to the present invention and FIG. 2 is a fragmentary cross-sectional View, in an enlarged scale, showing the engagement between a hollow rotary cylinder and a roller of the pellet mill shown in FIG. 1 and also the detailed structure of the roller.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will be described in further detail with reference to the accompanying drawing.

Referring to FIG. 1, a powdery material fed from a supply hopper 1 is led into the interior of a perforated hollow cylinder 3 through a supply hood 2 connected to the front end wall of said cylinder 3. The perforated hollow cylinder 3 is mounted on a ange of a hollow rotary shaft 6 through -a fixture 5, and rotated by said hollow rotary shaft 6 when the latter is driven by a prime mover not shown. A roller 4 is disposed in the cavity of the perforated hollow cylinder 3 in contact with or in slightly spaced relation to the inside wall surface of said cylinder, and secured to roller supporting members 9, 10 fixed on a lixed rod 7.

As shown in FIG. 2, the perforated hollow cylinder 3 is provided with a gear 16 at a portion thereof, while a cooperating gear 17 is provided on the surface of the roller 4, the arrangement being such that when the perforated hollow cylinder 3 is rotated, the roller -4 is driven at a predetermined speed ratio. The xed rod 7 has an axial fbore 8 extending therethrough and this laxial bore is in communication with the interior of the roller 4 through an oil supply tube 11 and an oil supply passage 13 formed in a roller shaft 12. Thus, it will be understood that a liuid compressed by fluid compressiing means not shown and fed into the axial bore v8 from one end thereof, is supplied into the interior of the roller `4f. The fluid introduced into the roller 4 is retained therein at a predetermined pressure by means of pressure retaining rings 14, 15 provided in said roller.

According to the present invention ywherein the roller is driven forcibly by the perforated hollow cylinder at a predetermined speed ratio as described above, binding of the roller can be prevented and further the powdery material being processed is subjected to not only compression but also a suitable degree of kneading action, so that the power consumption can be reduced markedly compared with the conventional device.

Further, according to the present invention, intrusion of the powdery material into the interior of the roller can be prevented completely by the pressure fluid supplied and retained in said roller and thereby the present pellet mill is capable of continuous operation for a period ranging from at least one week to several weeks, compared with the conventional pellet mill which is capable of continuous operation for only several hours.

By employing the pellet mill of this invention, it is possible to granulate powdery materials, e.g., urea high- Diameter of perforations in the hollow cylinder: 2.0 mm. Operating power: 0.04 kw./ kg.

In Examples 1 and 2, the pellet mill was continuously operated for 70 hours while maintaining the uid in the roller at a pressure of 3 kg/cm.2 and after the operation analysis compound fertilizers, the granulation of which 5 no change was observed interior of the mill, whereas in has been almost impossible by the conventional extrusion the control example, the pellet mill went slightly out of granulating method. As is obvious, the pellet mill of the Order after 2 hours of continuous operation and became present invention is applicable to the mass production of IlOPefaVC after 3 hOUfS- UPOII Overhaul the H1111, 1 YVaS a pellet of not only fertilizers but also many other similar reValed that the roller had been bound .by the fertihzer powdery materials, such as animal feeds, agricultural and further a large amOUIl 0f ne fellllef Powder Was chemicals and catalysts. present in the rotating mechanism of the roller.

Examples provided below show a comparison between EXAMPLE 3 the performance of the present pellet mill and that of the d conventional one, when used for the granulation of fer- Powdery mammal use tilizers. Examples 1 and 2 are the cases wherein the roller The high-analysis compound fertilizer as used in Ex- Was rotated forcibly, whereas the Control Example is the ample 1.

Fluid pressure in the roller 0 lig/cm.2 G.- 0.2 kg./em.2 G." 3 kg./cm.2 Gr Period of continuous operation 3hours Ghours 70 hours. Amount of fertilizer powder intruded Large Slight None.

into the roller.

case wherein the roller was let to slidably contact the cylinder. Example 3 is the case wherein a pressure iluid was supplied and retained in the roller during the operation.

EXAMPLE l Powdery material used Weight Ingredient Unit percent Potassium chloride. 60 258 25. 1

Urea 46 265 25. 7

Ammonium sulfate.- 21 95 9. 2

Double superphosphate 38 407 40. 0 Water 4 percent Roller peripheral speed/ hollow cylinder peripheral speed:

Thickness of the hollow cylinder: 15 mm.

Diameter of perforations in the hollow cylinder: 2.0 mm.

Operating power: 0.025 kw./kg.

EXAMPLE 2 Powdery material used Organic fertilizer composed of Roller peripheral speed/hollow cylinder peripheral speed:

Thickness of the hollow cylinder: 1.5 mm.

Diameter of perforations in the hollow cylinder: 2.0 mm.

Operating power: 0.02 kw./kg.

CONTROL EXAMPLE Powdery material used The same high-analysis compound fertilizer as used in Example 1. Roller peripheral speed/ hollow cylinder peripheral speed:

1.0 (The roller was rotated by sliding contact with the cylinder.) Thickness of the hollow cylinder: 25 mm.

In this example, a mixture of a lubricant and air was used as the pressure fluid to be supplied into the roller.

What we claim is:

1. An extrusion-type pellet mill wherein one or a plurality of rollers are disposed in the cavity of a hollow rotary cylinder having a number of apertures perforated through the wall thereof and rotated therein for thereby extruding a powdery material through said apertures in the form of pellet, said pellet mill comprising a gear provided on the surface of each one of said rollers, a gear provided on the inside wall surface of said hollow cylinder and intermeshing with said first gears on the respective rollers thereby to forcibly rotate said rollers at a predetermined speed ratio as said hollow cylinder rotates, and means for supplying a pressure fluid into the interior of each one of said rollers and retaining the same interior of said roller thereby to prevent intrusion of the powdery material into the interior of said roller during operation of the pellet mill.

2. An extrusion-type pellet mill comprising a rotary perforated cylinder as a die ring, one or a plurality of rollers rotatable within said die ring for extruding a powdery material through said die ring, gear means for rotating said rollers in engagement with said die ring, said gear means comprising a gear provided on the outer surface of said rollers and a gear provided on the inner surface of said die and being so arranged that said gears may intermesh with each other to forcibly rotate said rollers at a predetermined speed ratio as said die ring is drive.

3. An extrusion-type pellet mill as claimed in claim 2 and further including means for supplying a pressure uid into the interior of each of said rollers, to prevent the powdery material from intruding into the interior of said rollers during operation of the pellet mill.

References Cited UNITED STATES PATENTS 2,295,743 9/ 1942 Mealsin 18-12 2,757,621 8/1956 Johnson 18-12X 2,778,323 1/1957 Money 18--12X 3,045,280 7/ 19612 Bonnajoux 18-12 3,280,426 10/ 1966 Mealsin 18-12 `IAMES M. MEISTER, Primary Examiner 

